the rescue workers paused, and across scandinavia the moment was marked. then, by the field of flowers at the cathedral,. some people began to sing the words of a famous poem written for the young people of norway. ♪ >> brown: hours before he carried out his attacks, anders breivik published an extended manifesto on the internet. it detailed his belief, among other things, that islam poses an existential threat to european culture, and that many politicians are complicit in allowing that to happen. we talk about breivik and the broader issue of extremism with jonathan birdwell, a researcher at demos, a british think tank. his latest book, "the edge of violence," looks at the relationship between violent and non-violent radicals in europe and canada. and david art, an associate professor of political science at tufts university.